1. Field of the Invention
This invention relates to a hydraulic steering device having a steering angle transmitter and which is in communication with a steering valve. As a function of the actuation of the steering angle transmitter, the steering valve controls the communication between a steering drive, e.g., a steering cylinder, with a hydraulic pressure source and a reservoir. A correction device provides a synchronization between the position of the steering angle transmitter and the position of the steering drive.
2. Technical Considerations
Hydraulic steering devices in which a steering valve is actuated by a steering angle transmitter (for example a steering wheel) and controls the pressurization of a steering drive (for example of a steering cylinder actively connected to a steering axle with the steered wheels) are used in industrial vehicles, such as construction machines or industrial trucks. On known hydraulic steering devices of this type, there can be discrepancies between the position of the steering drive and the position of the steering angle transmitter (e.g., a steering wheel) as a result of leakage in the steering valve and/or the steering cylinder.
As a result of this leakage, the rotational position of the steering wheel and the position of the steered wheels do not always coincide and are, therefore, sometimes unsynchronized. In particular for the straight-ahead travel position of the steering wheel, different rotational positions of the steering wheel can occur as a result of the leakage. By “straight-ahead travel position” is meant the position of the steering wheel to make the vehicle move forward in a straight path. For an operator of an industrial vehicle of this type, this can lead to unpleasant situations since the correspondence between the rotational position of the steering wheel with the position of the steered wheels is not correct and stable. In addition, this lack of synchronization can lead to hazardous operating situations if the operator specifies the straight-ahead travel position from the steering angle transmitter but the vehicle moves in a curve on account of the unsynchronized correspondence between the position of the steering angle transmitter and the position of the steering drive. This operational behavior of known hydraulic steering devices can also lead to situations in which the operator must make constant corrections in the steering angle transmitter to maintain the desired direction of travel of the industrial vehicle as it travels a long distance straight ahead. As a result of which, the operator of such an industrial vehicle must maintain a high degree of concentration, which can lead to rapid fatigue.
Correction devices are known to synchronize the position of the steering angle transmitter with the position of the steering drive in hydraulic steering devices and, thus, to make possible a synchronization between the position of the steering angle transmitter and the position of the steering drive. In these known correction devices, the position of the steering angle transmitter (and thus the set-point for the steering deflection) is measured by means of an absolute sensor located on the steering angle transmitter. The current value of the steering deflection is determined by means of another absolute sensor located on the steering drive, for example on the steering cylinder. These absolute sensors are in communication with an electronic control device in which a constant and continuous comparison of the set-point and the actual value of the steering deflection is performed. Therefore, in the event of a discrepancy between the position of the steering drive and the position of the steering angle transmitter, it becomes possible to re-establish a synchronization of the steering drive with the position of the steering angle transmitter. Absolute sensors of this type (such as proportional sensors that measure the position of the steering angle transmitter and the position of the steering drive) and the corresponding electronic control device are complex and expensive to manufacture. As a result of which, a hydraulic steering device with such a known correction device is relatively expensive to manufacture.
Therefore, it is an object of the invention to provide a hydraulic steering device with a correction device which makes it possible to achieve synchronization between the position of the steering drive and the position of the steering angle transmitter but with lower design and manufacturing costs than known systems.